Well slip assembly

ABSTRACT

A slip mechanism for gripping a well string in a snubbing operation or the like, and in which the orientation of the slips relative to a surrounding slip bowl is controlled positively by movably connecting each slip to the bowl at two spaced locations, desirably through a swinging arm connection at one location and a guideway and interfitting projection at the second location.

United States Patent 1 1191 Spiri 1451 Nov. 12, 1974 WELL SLIP ASSEMBLY 1.o5o 1o1 11/1927 Taylor 24/263 CA l,674.l44 6/1928 Trnves.. 24/249 DP [75] Inventor. Will H. Splll, Whnuer, Ca ,762,037 6/l930 Taylor 1. 24 249 DP [73] Assignee: The Cavins Co., Long Beach, Calif.

- Primarv Evaminer-Donuld A. Griffin 22 l 20, l 73 l 1 Fl ed Aug 9 Attorney. Agent, or FirmW1ll1am P. Green [21] Appl. No.: 390,002

[57] ABSTRACT [52] US. Cl. 24/263 CA [51] Int. Cl E2lb 19/06 A shp mechamsm for gnppmg a Smng m a Snub [58] Field of Search 166/775 76, 75; 294/90, bing operation or the like, and in which the orienta- 294/l02 R, 102 24/249 DP, 263 D, 263 tion of the slips relative to a surrounding slip bowl is DA 263 D5, 263 CA, 263 D6 263 KH 263 controlled positively by movably connecting each slip QT 263 OK to the bowl at two spaced locations, desirably through a swinging arm connection at one location and a 5 References Cited guideway and interfitting projection at the second l0- UNITED STATES PATENTS 1,506,581 8/1924 Halley 24/263 CA 13 Claims, 11 Drawing Figures 47 47 2'70 7! 49 4 "1 1 5 s2 1 ..1 r 1 o 11. 55 EEz ifi T6 1 1 E 55 I70 E E E E 59 I '1 5e, 5e a7 4o 64 11 68a 40 I I I 35 I '47 E E 47 60 I E E '65 1 i E E 5 E 4 e 5' E E 5 E 63 l" o I 2617 480. 42 I l 7 GI 24: 14b 61 46 l 947 T 45 69 11 1o PATENTEUuuv 12 1914 3.8

summr a 46877 PAIENIED IIUV 12 I974 sum 3 BF 3 WELL SLIP ASSEMBLY BACKGROUND OF THE INVENTION This invention relates to slip assemblies for gripping a well pipe and holding it against axial movement. The slip assemblies embodying the invention have been in certain respects designed especially for use in snubbing operations, and will be described primarily as applied to that type of use. However,-it will be apparent that the disclosed apparatus may also be employed for gripping a string in other types of well equipment.

In a snubbing spider, a number of slips are mounted movably within a surrounding tapered slip bowl structure for generally axial relative movement, between active positions in which the slips grip and hold a well string and retracted positions releasing the string for vertical movement. The usual snubbing rig employs several such spiders, some of which act to support the weight of the string against gravity when active, while others are inverted to hold the string against upward movement. As a result of this inversion, conventional slip assemblies do. not function in this use to grip and release the string as effectively and controllably as would be desired, and in fact often interfere with the desired movements and manipulations of the string, largely because when inverted the positions and'orientations of the slips relative to the bowl andstring are not controlled positively enough, and the effect of gravity on the inverted slips is often to swing them radially inwardly to positions in which they obstruct and interfere with the string movements.

SUMMARY OF THE INVENTION The general purpose of the present invention is to provide an improved slip assembly which can control the positioning and orientation of the slips relativeto the slip bowl much more positively and effectively than in prior equipment. The invention accomplishes this result by attaching each slip to the bowl movably at two different locations, by two different connections spaced generally axially apart. By virtue of this double connection type of mounting, the orientation of the slips relative to the bowl structure is controlled positively at all times to prevent interference by the slip structure with the well string.

One of the two connections for mounting each slip preferably includes a guideway carried by the bowl or slip (desirably the former) and movably receiving and guiding an interfitting structure carried by the other of these parts. This guideway may extend along, and be formed essentially in, one of two engaging tapered camming surfaces of the bowl and slip, and may taper in correspondence therewith. The guideway may have a side wall containing an undercut groove for retaining and guiding a contacted interfitting part. For best results, both of two adjacent slips have lugs projecting into a common guideway in the slip bowl structure and guided for movement together while at the same time being free for some limited relative movement. A pin may extend through both of these lugs and have its opposite ends received and guided within two parallel undercut grooves in opposite side walls of the guideway. The guideway may curve progressively radially outwardly away from the well string at the larger end of the slip bowls tapered opening, to further remove the slips in their retracted positions from close proximity with the well string.

The second connection which mounts each slip may include a swinging arm movably mounted to the slip bowl and acting on swinging movement to control movement of a connected portion of the slip between active and retracted positions. As this arm turns about its axis in a retracting direction, the attached portion of the slip may move first generally axially and then move more in a radially outward direction to maximize outward retraction of the slip for a particular range of axial movement.

A pair of adjacent slips may be mounted movably by the same swinging arm, and the same guideway, for actuation in unison. The complete slip assembly may include two such pairs of slips, located at opposite sides of the well string, and having two swinging actuating arms connected operatively together for corresponding actuation by a common link element.

BRIEF DESCRIPTION OF THE DRAWINGS:

The above and other features and objects of the invention will be better understood from the following detailed description of the typical embodiment illustrated in the accompanying drawings, in which:

FIG. 1 is a fragmentary somewhat diagrammatic elevational representation of a well having snubbing apparatus utilizing spiders or slip assemblies embodying the invention;

FIG. 2 is an enlarged, elevational view of one of the spiders of the FIG. 1 apparatus;

FIG. 3 is a side elevational view taken on line 33 of FIG. 2;

FIG. 4 is a partial transverse section taken on line 4-4 of FIG. 3;

FIG. 5 is a perspective representation of the spider of FIGS. 2 to 4;

FIG. 6 is an enlarged plan view, partially broken away, of the spider showing the slips in their active positions;

FIG. 7 is a further enlarged vertical section taken on line 77 in FIG. 6;

FIG. 8 is an enlarged fragmentary horizontal section taken along line 88 of FIG. 7;

FIG. 9 is a perspective view showing the connections between one pair of slips;

FIG. 10 is a fragmentary section taken on line 10 10 of FIG. 7; and

FIG. 11 is a fragmentary view taken on line 11-11 of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows somewhat diagrammatically a snubbing or hydraulic workover apparatus to be used for raising or lowering, while under pressure, a tubular work string 13, which extends along a vertical axis 14 through a suitable well head structure 10 into a well 110. The well head may typically carry one or more blowout preventers 11, and have the usual annular rubber scraper 12 above the blowout preventers forming a pressure retaining seal with the outer surface of the work string. The apparatus of FIG. 1 includes four typically identical spiders 15, 16, 17 and 18 embodying the invention, two of which (spiders l5 and 16) are attached to the lower and upper sides respectivelyof a stationary platform 19, in relatively inverted positions, so that when these two spiders are in their active pipe gripping conditions of FIG. 1 they prevent downward and upward movement s respectively of the well string. The other two spiders 17 and 18 are similarly carried at the lower and upper sides respectively of a second platform 20 which is vertically movable between the fullline and broken line positions of FIG. 1. Platform 20 is power actuable between these positions by a number of fluid actuated piston and cylinder mechanisms 21, having power cylinders 22 connected to stationary platform 19 and pistons 23 attached to movable platform 20.

FIGS. 2 through 8 show in detail the construction and operation of one of the four identical spider assemblies, specifically spider 17 of FIG. 1. This spider includes four complementary slips 24a, 24b, 24c and 24d, mounted movably to an essentially annular rigid slip bowl structure 25. Each slip is arcuate about axis 14, and extends through approximately 90 degrees about that axis. The slips are movable between a retracted position illustrated in FIGS. 2 to 5, and an active pipe gripping position shown in FIGS. 6 and 7.

As seen best in FIGS. 2'through 5, the slip bowl 25 may be formed of two interconnected sections, including a main body part or section 26 extending almost entirely about the well string, and a gate section 27 closing an interruption 28 in body 26. The interruption 28 may be shaped to form a guideway into which the gate is slidable vertically to the position of FIG. in which it is suitably retained by a bolt extending through registering openings in sections 26 and 27 and carrying a nut 30. Interfitting axial dovetail grooves 127 and ribs 227 on sections 26 and 27 guide the gate for only axial movement relative to body 26. The upper surface 31 of the slip bowl structure 25 may be planar and disposed horizontally, and be retained upwardly against a horizontal undersurface 32 of platform (FIGS. 2 and 3) I by retaining bolts 33 extending through openings 34 in an upper flange portion 35 of the slip bowl structure.

. Internally, the two section slip bowl structure forms a central vertically extending passage 36, defined by an upwardly tapering frustoconical cam surface 37 which is centered about axis 14 and is formed partially on the main bowl section 26 and partially on gate section 27. This cam surface tapers at a uniform angle a with respect to axis 14 from the location designated 38 in FIG. 7 to the upper location 39. The slips 24a, b, c and d have corresponding frustoconically tapered complementary external surfaces 40, which in the FIG. 7 active gripping positions of the slips engage bowl surface 37 over an extended area in a relation camming the slips inwardly against the well string in response to upward movement of the slips. At their radially inner sides, the slips have complementary gripping faces 41 provided with arcuate teeth 42 following generally the curvature of the external cylindrical surface of the well string to effectively grip that string and prevent its relative upward movement in the FIG. 7 active condition of the slips. To enable replacement of the gripping teeth when worn, each slip may include an inner gripping die element 43 removably carried by the main body 44 of the slip. I

For mounting and actuating the slips, each slip has two upper and lower rigid mounting ears or lugs 45 and 46 projecting radially outwardly from the slip. All of these lugs are desirably flat or planar, being defined by parallel vertical planar opposite side faces 53 disposed parallel to a vertical plane 57 (FIG. 8) containing axis 14. The upper lugs 45 of the slips project radially outwardly into two diametrically opposed guideways 47 formed in the slip bowl structure 25 and are guided thereby for movement parallel to tapered bowl surface 37. The lower lugs 46 are connected to and actuated by a'pair of swinging arms 48 and 48a actuable by a piston and cylinder mechanism 49 carried by the slip bowl structure. The lugs may also serve the secondary purpose of connecting the slips together in pairs, for actuation of the slips between active and retracted positions essentially together while still permitting slight relative shifting movement of the two slips of each pair for optimum contact with the bowl and the gripped well string.

FIG. 9 shows one of the pairs of slips (24a and 24b) and the manner in which the lugs 45 and 46 of these slips are connected together, As seen in that Figure, the upper lug 45 of slip 24a is received near and parallel to, but spaced slightly horizontally from, the corresponding lug 45 of slip 24b, with a cylindrical horizontal guide pin 50 (FIGS. 7 and 8) extending through registering apertures 51 in the adjacent lugs 45. An annular flat washer 52 may be received about the pin between the spaced parallel vertical inner faces 53 of the lugs, to space them apart slightly. The pin may be slightly smaller in diameter than are the circular openings 51 and 54 in the lugs and spacer, to give the slips the desired freedom for some limited bodily shifting movement relative to the pin and relative to one another.

Each of the guideways 47 has a radially outer wall 56 andtwo opposite side wall surfaces (FIG. 8). These side walls are desirablyplanar and parallel to one another, and spaced equal distances from and parallel to the previously mentioned intermediate vertical plane 57 containing axis 14. The spacing s between the two side walls 55 of the guideway is slightly greater than the combined thicknesses of the lugs 45 and spacer 52 to further allow the discussed relative shifting movement of the connected slips.

To receive and guide the opposite ends of cylindrical pin 50, sidewalls 55 are undercut to form two parallel guide grooves 58, which may have the essentially rectangular horizontal sectional configuration of FIG. 8 dimensioned in. correspondence with the received portions of the pin. The pin and guide-way walls may be appropriately hardened to perform their guiding functions without execessive wear. Through most of the length of each guideway 47, and specifically from the location 38 of FIG. 7 to the location 39, the longitudinal axis 59 of the guideway (FIGS. 7 and 8) tapers at the same angle a with respect to axis 14 as does bowl surface 37, with the pin 50 and its grooves 58 being so located as to hold slip surfaces 40 in essential contact with bowl surface 37 as the slips retract downwardly from the FIG. 7 position. Downwardly beyond the location 38, the two guideways 47 curve progressively and arcuately radially outwardly at 147 about two parallel horizontal axes 447, to extend in opposite directions away from axis 14, toward extremities 247 of the guideways at which the guideways open generally radially outwardly (see FIGS. 5, 7 and 11). These lower curved portions of the guideways may be formed in two diametrically opposed downwardly extending curved projections 347 formed by the lower portion of the slip bowl body 26. I

The two lower lugs 46 of slips 24a and 24b are, like upper lugs 45, received closely adjacent one another, and are connected loosely together by two parallel horizontal bolts or pins 60 and 61. The upper of these pins 60 extends through a slot 62 formed in one of the previously mentioned actuating arms 48 or 48a, to form essentially a pivotal connection between the arm and lugs 46, causing these lugs and the lower ends of the slips to swing downwardly and outwardly about the horizontal axis 63 of arm 48 as the arm swings from its FIG. 7 position to its FIG. 4 position. Slot 62 is elongated radially of axis 63, to allow for some slight bodily shifting of lugs 46 relative to arm 48 as the arm swings. Each bolt 60 and 61 extends through apertures in lugs 46 which are large enough to allow slight orientation changing movement of the lugs relative to one another and relative to the pin. Also the head at one end of each bolt and the nut at its opposite end are spaced apart farther than is necessary to accomodate the lugs and the intermediate arm 48, to thus further assure a freedom for movement of the slips relative to one another. If desired, two coil springs 148 may be received about bolt 60 between lugs 46 and the bolt head and nut respectively, to yieldingly urge the lugs inwardly against arm 48 The arm 48 is mounted for its swinging movement about axis 63 by rigid connection to a horizontal shaft 64, which is journalled by two bearing lugs 65 carried by bowl body 26 to turn about axis 63. An outer end of shaft 64 is rigidly connected to a crank arm 67, which is pivotally connected at 68 to one end of a rigid link 69, whose opposite end is connected essentially pivotally at 70 to the end of the piston rod 71 of the piston and cylinder mechanism 49 carried by the slip bowl body. The piston rod and its connected piston 72 are movable horizontally in either direction along an axis 73 by pressure fluid fed selectively into the opposite ends of cylinder 74 from an appropriate three way control valve 75 or the like receiving pressurized fluid from a fluid source represented at 76 (FIG. 5).

As will be understood, when piston 72 moves rightwardly in FIG. 2, the resultant rightward movement of link 69 causes arm 67 and the connected arm 48 to swing in a counter-clockwise direction from the FIGS. 2 and 3 retracted slip position to the FIG, 7 active slip position. The same rightward movement of link 69 causes clockwise swinging movement of the corresponding arms 67a and 48a which are connected to and actuate the second pair of slips 24c and 24d at the right side of FIG. 2. To attain this result, link 69 is pivotally connected to crank arm 67a at a location 68a which is above the axis 63a of arm 48a, rather than beneath the axis as in the case of arm 48. Except for this reversed manner of connection of the second pair of slips to link 69, the mounting and actuation of slips 24c and 24d is identical to that of slips 24a and 24b discussed above in detail. The essentially pivotal connection 70 between piston rod 71 and link 69 may include a vertically extending slot 170 in link 69 movably receiving a pin 270 carried by rod 71 to enable slight vertical movement of the link at connection 70 relative to the piston rod in order to compensate for the swinging movement of the link at connections 68 and 68a about axes 66 and 66a. In the FIG. 7 positions of actuating arms 48 and 48a, these arms may project inwardly essentially horizontally, and be received partially within the lower curved portions of guideways 47, and within cutaways 547 formed in the bowl structure radially outwardly of and above the. lower curved extremities of the guideways. As seen in FIGS. 7 and 11, the radially outer wall 56 of each guideway 47 may be broken away at the locations of the cutaways 547, and specifically walls 56 may terminate downwardly at the locations 647 of FIG. 7, to allow for such reception of the arms 48 and 48a in the guideways and cutaways.

To now describe a cycle of operation of the equipment of FIG. I, assume for example that it is desired to progressively remove the work string 13 from well while under pressure. Assume also that the two lower spiders 15 and 16 are in their actuated pipe gripping conditions of FIG. 1 so that spider 15 holds the string against upward movement and spider 16 prevents downward movement. With the string thus retained, and the slips of the spider 15 and 16 in their retracted conditions of FIGS. 1, 2, 3 and 4, the upper platform and spiders 15 and 16 are actuated downwardly by power units 21 to their FIG. 1 positions, and the spiders 15 and 16 are then actuated to their gripping conditions while spiders 17 and 18 are released. The platform 20 may then be moved upwardly to raise the string a predetermined distance, following which the conditions of the four spiders may be reversed, to allow the movable platform to move downwardly again for a repeat of the entire process, to move the string upwardly through another step, etc. Downward movement of the string can be accomplished in areverse manner.

Each time that a particular spider is actuated from one of its conditions to another, the piston rod 71 of FIG. 2 acts by rightward or leftward movement to correspondingly displace link 69 rightwardly or leftwardly, and swing arms 67 and 67a, and the attached arms 48 and 48a, in opposite rotary directions. This swinging movement of arms 48 and 48a moves the four slips upwardly or downwardly between the released FIG. 2 position and the active FIG. 7 position. In moving between these positions, the outer surfaces 40 of the slips follow closely along and remain approximately in contact with the inner tapering surface 37 of the slip bowl, until the slips near the lower portions of their travel, at which the slips swing rapidly outwardly generally tangentially with respect to the inner curved surfaces 447 of the guidway lugs 347 to the outwardly retracted inclined positions of FIGS. 2 and 4. In these positions, the slips are located sufficiently far from the axis 14 to effectively avoid any possible interference with or obstruction of the string 113, and yet this full retraction is attained with a minimum of vertical movement of the slips. Further, the unique mounting of each of the slips at two axially spaced locations maintains each slip at all times under complete positional control, so that even though the assembly is inverted from the normal condition of a slip assembly, the orientation of the slips is positively controlled and they can not in any position swing inwardly into the path of the well string.

I claim:

1. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said second connection including means forming a generally axially extending guideway in said slip bowl structure which converges progressively toward said axis as it advances axially, and interfitting means carried by said one slip structure and projecting into and movable along said guideway, said guideway having a first portion extending at essentially a uniform angle to said axis, and having an. end portion curving progressively away from the axis.

2. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bow] at said two spaced locations, said second connection including means forming a generally axially extending guideway in said slip bowl structure which converges toward said axis, and interfitting means carried by said one slip structure and projecting into and retained within and movable along said guideway, said interfitting means comprising a lug projecting generally radially outwardly from said one slip structure into said guideway, and a pin extending through and retained by said lug, said guideway having two opposite side walls containing two undercut grooves, and guidably receiving opoosite ends of said pm.

3. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said second connection including means forming a guideway in said bowl structure, and two lugs projecting from said one slip structure and from an adjacent second slip structure into said guideway and both guided for movement therealong, said lugs being free for limited movement relative to one another within said guideway.

4. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said, bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said first connection comprising a swinging arm attached to said bowl structure for swinging movement, two adjacent lugs formed on said one slip structure and on an adjacent second slip structure, and means connecting said lugs essentially pivotally to said arm for actuation thereby but allowing limited relative adjusting movement of the two slip structures.

5. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said structures having engaging tapering camming surfaces, said first connection including an arm mounted to said bowl structure for swinging movement relative thereto and connected essentially pivotally to said one slip structure and to an adjacent second slip structure to actuate them essentially in unison but enabling limited relative movement of the two slip structures, said second connection including means forming a guideway in said bowl structure recessed outwardly beyond said tapering surfaces and following essentially the taper thereof, and lugs on said one slip structure and said second slip structure projecting into and movably guided by said guideway and free for limited relative movement, and powered means for actuating said swinging arm to move said one slip structure and said second slip structure generally axially.

6. A slip assembly as recited in claim 5, including means forming a second pair of said first and second connections essentially diametrically opposite said first pair of connections for movably mounting a second pair of said slip structures while allowing limited relative movement thereof, said second pair of connections including 'a second of said swinging arms and a second guideway; there being linkage operatively connecting said two swinging arms together for pivotal movement in opposite directions to actuate their respective slip structures essentially in unison.

7. A slip assembly as recited in claim 6, in which each of said second connections includes a pin in one of said guideways extending through apertures in said lugs of two associated slip structures with some looseness and having opposite ends guidably received within two parallel undercut guide grooves formed in two opposite side walls of the guideway.

8. A slip assembly as recited in claim 7, in which said guideways have ends which curve progressively away from said axis and open essentially radially outwardly away from the axis.

9. A slip assembly for gripping a tubular well string, extending along an axis; comprising a slip bowl structure, a plurality of slip structures; said bowl structure and said slip structures having tapering surfaces engaging in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof; an arm mounted for swinging movement relative to said bowl structure and connected to a first portion of one of said slip structures at a first location in a relation causing said portion, upon swinging movement of the arm, to move between an active string gripping position and a retracted position; a connection attaching a second portion of the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location; said connection including a guide structure carried by said bowl structure, and co-acting means carried by said one slip structure and interfitting with said guide structure for guided movement generally axially thercalong; said guide structure having a first portion directing said co-acting means along a path disposed at essentially a uniform angularity with respect to said axis, and having a second portion therebeyond directing said co-acting means along a path which curves progressively away from said axis at an increasing angularity with respect thereto.

10. A slip assembly as recited in claim 9, including powered means for actuating said slip structures generally axially between active string gripping positions and retracted positions.

11. A slip assembly as recited in claim 10, in which said powered means comprise a fluid actuated piston and cylinder assembly.

12. A slip assembly as recited in claim 9, in which said guide structure is a guideway formed in said slip bowl structure and recessed radially outwardly thereinto beyond said camming surfaces, said coacting means including a guide unit carried by said one slip structure and projecting outwardly therefrom past the diameter of said camming surfaces and into said guideway and guided thereby for movement along the guideway first at said uniform angularity to the axis and then at said increasing angularity.

13. A slip assembly as recited in claim 9, including means attaching a second of said slip structures to said one slip structure at both of said first and second locations for movement with said one slip structure between said positions but allowing limited relative adjusting movement of the two slip structures. 

1. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said second connection including means forming a generally axially extending guideway in said slip bowl structure which converges progressively toward said axis as it advances axially, and interfitting means carried by said one slip structure and projecting into and movable along said guideway, said guideway having a first portion extending at essentially a uniform angle to said axis, and having an end portion curving progressively away from the axis.
 2. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said second connection including means forming a generally axially extending guideway in said slip bowl structure which converges toward said axis, and interfitting means carried by said one slip structure and projecting into and retained within and movable along said guideway, said interfitting means comprising a lug projecting generally radially outwardly from said one slip structure into said guideway, and a pin extending through and retained by said lug, said guideway having two opposite side walls containing two undercut grooves, and guidably receiving opoosite ends of said pin.
 3. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection aTtaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said second connection including means forming a guideway in said bowl structure, and two lugs projecting from said one slip structure and from an adjacent second slip structure into said guideway and both guided for movement therealong, said lugs being free for limited movement relative to one another within said guideway.
 4. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, and a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said first connection comprising a swinging arm attached to said bowl structure for swinging movement, two adjacent lugs formed on said one slip structure and on an adjacent second slip structure, and means connecting said lugs essentially pivotally to said arm for actuation thereby but allowing limited relative adjusting movement of the two slip structures.
 5. A slip assembly for gripping a tubular well string, extending along an axis, comprising a slip bowl structure, a plurality of slip structures engaging said bowl structure in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof, a first connection attaching one of said slip structures to said bowl structure movably at a first location for generally axial relative movement between an active string gripping position and a retracted position, a second connection attaching the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location and in a relation positively controlling its orientation during shifting movement by the movable attachment of the slip structure to the bowl at said two spaced locations, said structures having engaging tapering camming surfaces, said first connection including an arm mounted to said bowl structure for swinging movement relative thereto and connected essentially pivotally to said one slip structure and to an adjacent second slip structure to actuate them essentially in unison but enabling limited relative movement of the two slip structures, said second connection including means forming a guideway in said bowl structure recessed outwardly beyond said tapering surfaces and following essentially the taper thereof, and lugs on said one slip structure and said second slip structure projecting into and movably guided by said guideway and free for limited relative movement, and powered means for actuating said swinging arm to move said one slip structure and said second slip structure generally axially.
 6. A slip assembly as recited in claim 5, including means forming a second pair of said first and second connections essentially diametrically opposite said first pair of connections for movably mounting a second pair of said slip structures while allowing limited relative movement thereof, said second pair of connections including a secOnd of said swinging arms and a second guideway; there being linkage operatively connecting said two swinging arms together for pivotal movement in opposite directions to actuate their respective slip structures essentially in unison.
 7. A slip assembly as recited in claim 6, in which each of said second connections includes a pin in one of said guideways extending through apertures in said lugs of two associated slip structures with some looseness and having opposite ends guidably received within two parallel undercut guide grooves formed in two opposite side walls of the guideway.
 8. A slip assembly as recited in claim 7, in which said guideways have ends which curve progressively away from said axis and open essentially radially outwardly away from the axis.
 9. A slip assembly for gripping a tubular well string, extending along an axis; comprising a slip bowl structure, a plurality of slip structures; said bowl structure and said slip structures having tapering surfaces engaging in a camming relation acting to cam the slip structures radially inwardly upon axial movement thereof; an arm mounted for swinging movement relative to said bowl structure and connected to a first portion of one of said slip structures at a first location in a relation causing said portion, upon swinging movement of the arm, to move between an active string gripping position and a retracted position; a connection attaching a second portion of the same slip structure to said bowl structure movably at a second location spaced generally axially from said first location; said connection including a guide structure carried by said bowl structure, and co-acting means carried by said one slip structure and interfitting with said guide structure for guided movement generally axially therealong; said guide structure having a first portion directing said co-acting means along a path disposed at essentially a uniform angularity with respect to said axis, and having a second portion therebeyond directing said co-acting means along a path which curves progressively away from said axis at an increasing angularity with respect thereto.
 10. A slip assembly as recited in claim 9, including powered means for actuating said slip structures generally axially between active string gripping positions and retracted positions.
 11. A slip assembly as recited in claim 10, in which said powered means comprise a fluid actuated piston and cylinder assembly.
 12. A slip assembly as recited in claim 9, in which said guide structure is a guideway formed in said slip bowl structure and recessed radially outwardly thereinto beyond said camming surfaces, said coacting means including a guide unit carried by said one slip structure and projecting outwardly therefrom past the diameter of said camming surfaces and into said guideway and guided thereby for movement along the guideway first at said uniform angularity to the axis and then at said increasing angularity.
 13. A slip assembly as recited in claim 9, including means attaching a second of said slip structures to said one slip structure at both of said first and second locations for movement with said one slip structure between said positions but allowing limited relative adjusting movement of the two slip structures. 